The present invention relates to devices for deploying body implantable prosthesis intended for fixation in body lumens, and more particularly to the delivery and placement of radially self-expanding stents or other radially expandable stents.
Certain prosthesis known as radially self-expanding stents are useful in a variety of patient treatment and diagnostic procedures, for fixation in blood vessels, biliary ducts and other lumens to maintain the passages. A highly preferred construction for a radially self-expanding stent is a flexible tubular braided structure formed of helically wound thread elements, as disclosed in U.S. Pat. No. 4,655,771 (Wallsten). Wallsten teaches use of a catheter for delivering the stent to the intended treatment site. A pair of grips maintain the stent at the distal end of the catheter and are controlled by an operational member at the proximal end of the catheter to release the stent after positioning and initial medial stent self-expansion.
Another approach to deploying self-expanding stents is shown in U.S. Pat. No. 4,732,152 (Wallsten et al) and in U.S. Pat. No. 4,848,343 (Wallsten et al). Often referred to as the "rolling membrane" method, this approach utilizes a tubular membrane folded over upon itself to provide a double wall for maintaining a self-expanding stent at the distal end of the catheter. The outer wall of the membrane is movable proximally to expose the stent and allow a radial self-expansion, beginning at the distal end of the stent. More particularly, one end of the membrane is attached to an inner catheter or probe, and the other end of the membrane is connected to an outer catheter that surrounds the probe. When the outer catheter is moved proximally relative to the inner catheter, it moves the outer wall of the membrane proximally as well, to expose the stent and allow radial self-expansion.
Yet another approach is shown in PCT patent application, Publication No. WO 94/15549 entitled "Method for Deploying Body Implantable Stent". This application describes several stent deployment devices employing interior and exterior catheters to deploy prostheses including radially self-expanding stents. One of these versions (FIGS. 9-13) employs a rolling membrane controlled through manipulation of the catheters to release a stent for self-expansion.
Stents constructed of a recovery metal, e.g. an alloy of titanium and nickel such as that sold under the brand name Nitenol, can be used in lieu of radially self-expanding stents for certain applications. A recovery metal stent may be formed initially in an expanded radius configuration, then plastically deformed while cool into a reduced radius configuration for delivery to a treatment site. Following delivery the stent is heated, which causes it to radially expand toward its original radius and into contact with tissue at the treatment site. Devices for delivering recovery metal stents and radially self-expanding stents can be constructed according to the same general principles.
While quite effective in certain applications, these devices generally incorporate interior catheters, probes or other members surrounded by the stent being deployed, and generally rely on a relatively rigid outer member, usually an exterior catheter, to surround and maintain the stent under radial compression. Such devices may be too large for deploying stents within narrower blood vessels and other body passages, and may be difficult to maneuver distally through serpentine passages defined by the body lumens.
Frequently during a procedure involving stent deployment, it is desired to force the stent against surrounding tissue after its deployment. This insures a more secure positioning of the stent, a more uniform lumen for fluid flow, and also more reliably establishes a final axial length (i.e. degree of axial contraction) of the stent. It is important during lesion treatment procedures to determine the final length (or degree of axial contraction) of the stent after self-expansion, to insure that a given stent is of sufficient length in relation to the lesion being treated. A dilatation balloon, mounted near the distal end of the catheter, can be used for this purpose. When using such a balloon, it would be desirable to provide protection against accidental bursting of the balloon either during or after its inflation.
Therefore, it is an object of the present invention to provide a device for deploying radially self-expanding stents, with sufficient axial rigidity yet enhanced flexibility for accommodating advancement through narrow and non-linear body passages.
Another object is to provide a reduced diameter stent retaining tip for a stent deployment catheter.
A further object is to provide a stent delivery apparatus that affords good axial stiffness and trying characteristics, whether steered through body passages or advanced over a guidewire.
Yet another object is to provide a device for delivering a radially self-expanding stent with a dilatation balloon expandable against the delivered stent to force it against surrounding tissue, and further incorporating a fluid tight membrane surrounding the dilatation balloon to afford added protection during high pressure dilatation procedures.